LHCBGAUSS-1089: Added parameter in Evtbs2llGammaISRFSR to cut on dimuon mass
A new dimuon minimum mass parameter has been added to the EvtGenExtras decay model Evtbs2llGammaISRFSR to improve generation efficiency. The default value is zero and the number of accepted parameters is now either 11 or 10, so that it is backward compatible with original decay files which only use 10 parameters.